1. Field of the Invention
The present invention relates to a display device, and in particular to a display device using a thin film transistor substrate.
2. Description of the Related Art
As a display device of an information communication terminal such as a computer and a television receiver, a liquid crystal display device is used widely. Further, an organic EL display device (OLED), a field emission display device (FED), and so on are also known as thin display devices. The liquid crystal display device is a device for displaying an image by varying the orientation of liquid crystal components, which are encapsulated between two substrates, using the variation in the electrical field to thereby control the level of the permeability of the light transmitted through the two substrates and the liquid crystal components.
In the display devices, which apply voltages corresponding to predetermined grayscale values to respective pixels of a screen, including such a liquid crystal display device, there are arranged thin film transistors for applying the voltages corresponding to the grayscale values to the respective pixels. In general, gates of the thin film transistors of the respective pixels corresponding to one line of the screen are connected to a single signal line (hereinafter referred to as a “gate signal line”), and a drive circuit is controlled to output voltages, which set the respective thin film transistors to a conductive state, sequentially to the gate signal line. Further, at an end portion of a display area, there are arranged dummy pixels outside the display area so that the structural and electromagnetic variation due to the fact that the end portion is located at the end of the display area does not affect the display.
JP 2010-097024 A discloses that switching elements are arranged outside the display area, and even in the case in which a static electrical charge occurs, the switching elements are broken to thereby protect the elements inside the display area.
JP 09-005780 A discloses that nondisplay pixels are arranged outside the display area, and pixel electrodes of one or more columns are eliminated so as not to cause the luminance variation in display and not to degrade the sealing performance of the liquid crystal in the liquid crystal display device.
Due to the demand of downsizing to electronic apparatuses in recent years, it is requested to reduce an outside area (hereinafter referred to as a “frame area”) of the display area. FIG. 11 is a diagram corresponding to a field of vision from the front of a liquid crystal display panel 800. The liquid crystal display panel 800 has a configuration in which a liquid crystal is encapsulated between a color filter substrate 810 and a thin film transistor (TFT) substrate 820, and is attached with a drive integrated circuit (IC) 830 for operating a circuit of the TFT substrate 820, and a flexible printed circuit (FPC) 840 for transmitting, for example, information of an image to be displayed to the drive IC 830.
FIG. 12 is a schematic diagram schematically showing a D part shown in FIG. 11, and shows a pixel electrode 821 inside a display area, and the state of the arrangement of dummy pixel electrodes 822 of respective dummy pixels outside the display area. FIG. 13 is a diagram schematically showing the state of the arrangement of the wiring of the dummy electrodes 822 and the periphery thereof in an F part shown in FIG. 12. As shown in FIG. 13, similarly to the pixel electrodes inside the display area, in the dummy pixels, the pixel is composed of a gate signal line 824 and an image data signal line 825, and the image data signal line 825 is connected to the dummy pixel electrode 822 via a tin film transistor 827. FIG. 14 is a cross-sectional view along the XIV-XIV line shown in FIG. 12. In the example shown in the drawing, the dummy pixel electrode 822 has a similar size to the pixel electrode 821 located inside the display area, and is arranged to be conductive with the image data signal line 825 when the gate signal line 824 is set to a High potential, and is arranged to be able to perform a similar operation to that in a display area 860. FIG. 15 shows an equivalent circuit in this case. A signal voltage transmitted through the image data signal line 825 is applied to the dummy pixel electrode 822, and causes an electrical potential difference with a common electrode 829.
However, also in the display device requiring such dummy pixels, a display device with a smaller frame is demanded, and further, for the sake of convenience of the operation of a gate signal drive circuit (not shown), it may become necessary to dispose a plurality of the gate signal lines 824 on the upper and lower outsides of the display area in some cases.